In the field of semiconductor packages and modules, a substrate with a die cavity to accommodate a semiconductor chip is rather common. The die cavity comprises a die-cavity sidewall and a die-attached plane. For controlling the height of the die-cavity sidewall and the coplanality of the die-attached plane, the die-cavity sidewall and the die-attached plane are manufactured from two different substrates firstly, then by using an adhesive layer to laminate the substrate with a die-cavity sidewall and the substrate with a die-attached plane for forming a laminated substrate assembly with a die cavity. As disclosed in U.S. Pat. No. 6,506,626 and U.S. Patent Application Publication No. 2001/0046725, the substrate with a die-attached plane is a ball grid array circuit board and the substrate with a die-cavity sidewall is a metal stiffener or spacer circuit board, both substrates are assembled to be a substrate assembly with a die cavity for manufacturing a semiconductor package or module with a faceup die cavity. As disclosed in U.S. Pat. No. 6,639,304 and U.S. Pat. No. 6,501,168, the substrate with a die-attached plane is a metal plate or metal core. Moreover, the substrate with a die-cavity sidewall is a circuit board with an opening or window. Both substrates are assembled for manufacturing semiconductor package or module with facedown die cavity.
Normally the adhesive layer used for laminating the two substrates mentioned above is acrylate film, liquid adhesive or prepreg. When the adhesive layer is a solid type or gummy type film such as acrylate film or prepreg, it is necessary to punch or route an opening, then two substrates are laminated under the opening of the adhesive layer aligned to the die-attached plane of the substrate. However, due to the nature of the adhesive layer, the adhesive layer will stick to the tooling or attract unwanted particles during processes, which caused extra cleaning problem for tooling and degradation of adhesion. Moreover, the arcylate film is very sensitive to moisture and only can reach JEDEC lever four. During the routing or punching processes, prepreg can be easily damaged and formed lots of resin flakes or particles.
When using liquid adhesive as an adhesive layer for bonding the two substrates mentioned above, as well known, the liquid adhesive needs to apply to the substrate with a die-cavity sidewall or to the substrate with a die-attached plane via screen printing. In order to avoid the contamination of liquid adhesive onto the die-cavity sidewall during laminating the substrates, the liquid adhesive must have higher adhesion with proper surface tension and viscosity. If the liquid adhesive contains solvent, after screen printing, the liquid adhesive layer will need pre-bake or drying processes and then the two substrates mentioned above are laminated and cured under higher temperatures. During the curing processes, the curing conditions need extremely under control, any mistakes may force the liquid adhesive layer to flow to the die-cavity sidewall or die-attached plane and cause the coplanality issue for die attachment.
A method for manufacturing die cavity on a substrate is disclosed in U.S. Pat. No. 6,195,264. An adhesive layer with photosensitive material can be applied between the metal stiffener and printed circuit board. A substrate assembly with a die cavity will be formed after lamination since the adhesive layer with photosensitive material can be exposed and developed, therefore, no residual of the adhesive layer can be found inside the die cavity. However, the requirements for the adhesive layer with photosensitive material should have an excellent photosensitivity and easy photo processing characteristics, moreover, good thermal-setting properties, adhesion, and heat conductivity. However, such kind of adhesive layer with photosensitive material is not easy to get which is in higher cost.